This disclosure relates to a charge compensation component having a drift path between two electrodes, an electrode and a counterelectrode, and methods for producing the same. The drift path has drift zones of a first conduction type and charge compensation zones of a complementary conduction type with respect to the first conduction type.
Charge compensation components of this type are known from the documents U.S. Pat. Nos. 4,574,310 and 5,216,275. The charge compensation components proposed therein have a drift path with drift zones and charge compensation zones, which are referred to as composite buffer layer (CB) in the document U.S. Pat. No. 5,216,275. Such charge compensation components having depletable complementarily doped charge compensation zones in the form of complementarily doped regions (e.g., pillars). These regions require a very precise setting of the charge compensation since the breakdown voltage that can be achieved is sensitively dependent on the degree of compensation set, as illustrated by the document U.S. Pat. No. 6,630,698 with FIG. 7.
In particular a charge compensation component having a constant degree of compensation, such as is known from the documents U.S. Pat. Nos. 4,574,310 and 5,216,275, illustrates these severe fluctuations in the breakdown voltage. Manufacturing faults that occur e.g., as a result of geometrical tolerances of the photolithography masks and/or as a result of fluctuation tolerances of the implantation doses in the layer-by-layer doping of epitaxial layers for the drift path with drift zone regions and charge compensation zone regions in particular in the compensation-sensitive regions can therefore cause an effect, which can be alleviated in part by a variable doping of the charge compensation zones by the provision of a multipercent p-type overdoping or n-type underdoping of the charge compensation zone in the compensation-sensitive region near the pn junction with the electrode and, for balancing, a multipercent n-type overdoping or p-type underdoping of the charge compensation zone near the counterelectrode, as is known from the document U.S. Pat. No. 6,630,698 B1.
In this respect, FIG. 10 illustrates a diagram for the degree K of charge compensation between SOURCE and DRAIN as a function of the drift path depth. A given degree K of charge compensation can be formed, on the one hand, by a difference between high n-conducting and p-conducting dopings or, on the other hand, by a difference between two low dopings.
What is common to both profiles (solid and dashed lines) of the degree of compensation in FIG. 10 (remain constant or variable) is that as the doping increases, the absolute faults in the doping during the production process likewise increase. Although the relative faults remain the same (lithography, implantation or deposition of doped epitaxial layers), the absolute faults increase on account of the higher doping levels.
The influence of faults in the setting of the degree of compensation is not the same everywhere in the component. Therefore, it is possible by using a suitable design of the degree of compensation, to produce a component which is significantly less sensitive toward manufacturing fluctuations. The influence of the manufacturing faults will be explained in greater detail below. The profile of the electric field strength of a component whose degree of compensation corresponds to the dashed profile in FIG. 10 illustrates a roof-shaped profile as in FIG. 3. The relationship between degree of compensation and field strength is given by Gauss' law, according to which the change in the electric field strength is proportional to the charge. In the off-state case, all the doping atoms are ionized; this means that in a region with p-type dopant excess, there is an excess of negatively charged doping atoms: the electric field rises in this region. According to analogous consideration, it falls in a region with an excess of n-type doping atoms.
If a disturbance in the form of an additional p-type doping is then introduced in a region of the component, this means, in the off-state case, additional charge, which in turn results in a local field gradient, that is to say leads to a step in the field strength profile. For the sake of simplicity, a disturbance that is localized exactly at a depth x is considered. If the breakdown voltage is present at the component, the field strength in the centre of the component (as viewed from source to drain) is equal to the breakdown field strength in a constant fashion. The steps in the field strength profile which are illustrated in FIGS. 4A and 4B result depending on the position of the perturbation doping in proximity to the source or drain.
Since the voltage corresponds to the integral of the field strength, a disturbance in proximity to the drain brings about an increase in the reverse voltage by the magnitude dE·dx, where dE is the height of the field strength step and dx is the distance between the step and the end of the space charge zone. The effect of such a disturbance on the breakdown voltage is therefore all the greater, the further the disturbance is from the end of the space charge zone. In other words: the component reacts more sensitively to disturbances in the degree of compensation in the centre (between source and drain), than in proximity to the source or drain.
One embodiment of the invention provides a charge compensation component having a first electrode, a counterelectrode and a drift path between the electrodes.
The drift path has drift zones of a first conduction type and charge compensation zones of a complementary conduction type with respect to the first conduction type. Furthermore, the drift path has a drift path layer doping including the volume integral of the doping locations of a horizontal drift path layer of the vertically extending drift path including the drift zone regions and charge compensation zone regions arranged in the drift path layer. This drift path layer doping is greater in the vicinity of the two electrodes than in the direction toward a central region of the drift path.
With this charge compensation component, the sensitivity toward manufacturing-dictated perturbation dopings is reduced in the region of the electrodes. The embodiment according to the invention of the drift path layer doping, which is lowest in a central region of the drift path and increases toward the two electrodes, results in an additional positive effect, namely that the breakdown characteristic curve has a reverse voltage reserve in the avalanche case, such that the “snap back effect” commences in delayed fashion.
For these and other reasons, there is a need for the present invention.